1. Field of the Invention
The present invention relates to apparatus and methods for in-flight correction of an inertial navigation system employed on an aircraft. More particularly, this invention pertains to the performance of such calibration over a body of water without resort to devices and signals generated by external sources.
2. Description of the Prior Art
The in-flight correction of an aircraft's inertial navigation system is complicated when the aircraft proceeds over a body of water. When flying over land, the navigation system can rely upon known monument locations to provide the necessary feedback for updating the navigation variables of the inertial system and thereby overcome the effects of inertial instrument (accelerometer, gyro) errors.
When the aircraft proceeds over water, it no longer can rely upon the monuments that prove so useful over land as benchmarks. Rather, externally-based radio navigation systems must be utilized. LORAN, for example, can provide the over-water pilot with signals indicative of the aircraft's position. By taking radio fixes from such a system the pilot may then periodically correct the on-board inertial navigation system and its instruments.
Unfortunately, the use of externally-generated radio signals is not always possible. Military applications, for example, must be take into account the risk of destruction of an external signal source, the need for radio silence and other potential disruptions to the use of externally-generated navigation signals.